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factors associated with the development of mental deficiency. They found that the rate of mental deficiency was approximately 40 per 1,000 among firstborn children, rising to 140 per 1,000 for fourth children, and then to 400 per 1,000 in sixth children-a tenfold increase over the rates in first children.
It is also appropriate here to quote a statement published by Dr. Cicely Williams:
.. . the "survival of the fittest" is a misapplied cliche. It was not recognized that the same conditions that will kill 30 percent of the babies in the first year of life will also produce a large proportion of persons with damaged lives who will be a burden for years and perish at a later date. (78, p. 1280)
Infant mortality rates are no longer so high; infant mortality attributable to family size was probably never that high, though it is interesting to note that in discussing population change in England in the eighteenth century McKeown said:
. . . Marriage rates were high in the eighteenth century and an increase in the birth rate would have been due chiefly to addition of children to existing families, rather than to an increase in the number of one-child families. Hence any increase in the birth rate would have been offset largely by an increase in postnatal mortality. (79, italics mine)
Even though mortality rates have declined since many of the studies relating them to family size were carried out, we know that such rates still prevail in many parts of the world, and there is no reason to doubt that the effects associated with family size are still present. Beyond that, we do know more now about the consequences that might be expected among the children who do not die. For example, the steadily accumulating knowledge concerning the permanent effects of malnutrition on the growth of the brain in young children (9) ought to give pause to anyone concerned about the human resources of a nation. The evidence here is such that any measure that might reasonably be expected to reduce the prevalence of malnutrition is worth supporting to the fullest extent possible.
Would reducing family size, or increasing birth interval, reduce the effects we have seen? Once again, the evidence available is inadequate for an unqualified answer. Such evidence as there is suggests an affirmative answer, derived from the fact that in those studies in which social class as well as family size were examined, the lower-class mothers who had only one or two children seem to have provided as well for their children as the upper-class mothers. This leaves unanswered, of course, the most important question: would the parents of large families have provided better for their children if